This invention relates in general to piezoelectric transducers and, in particular, to a piezoelectric transducer apparatus having independent gain and phase characteristic functions of the fourth-order partial differential equations.
Piezoelectricity is a phenomenon in which positive and negative electric charges appear on opposite sides of some non-conducting crystals when subjected to mechanical pressure. The converse piezoelectric effect, electrostriction, is the property of some non-conductors, or dielectrics, that deform slightly under the application of an electric field. Piezoelectricity and electrostriction are the reciprocating conversions of mechanical and electrical energy back and forth by piezoelectric workpieces that can be utilized in various applications such as vibration detection and actuation of controlled structures.
Traditional piezoelectric point sensors are used primarily for the detection and measurement of vibrations on a specific point on an examined structure. Shape and type of these piezoelectric sensors can be modified in order to meet the need for the detection of, for example, the vibration of an examined structure in the axial direction. Such sensors are easily customizable to various structural configurations and have been widely utilized in many applications.
However, these prior-art piezoelectric point sensors have a basic characteristic that limits their application. Frequency response characteristics of these point sensors are self-constrained by characteristics of their own structural configuration. For example, traditional point sensors are limited to their useful frequency response ranges due to their structural configuration characteristics. Electronic circuitries have to be employed based on the traditional filter theory. However, sensor frequency response characteristics are thus altered such that their usefulness jeopardized.
Further, these prior-art piezoelectric point sensors can only be useful for the detection of the structural characteristics of single points on an examined structure. One single-point sensor does not reveal the structural characteristics of an examined target in their entirety. When the scope of sense and detection for a target structure needs to be relatively large, excessive number of point sensors have to be installed. The resulted vast amount of information collected by these sensors presents processing problems for the detection system. As a result, utilization of large numbers of these point sensors in applications such as real time control of a structure becomes complicated and unrealistic.
On the other hand, since the emergence of distributed sensor theories in the 1980s, it has become clear that useful bandwidth of piezoelectric sensors can be designed and controlled flexibly to an extent. This is possible by control and adjustment in parameters such as shape and polarization direction of the electrode of a distributed sensor. Due to the fact that the electrode of a distributed sensor is distributed continuously over an extent in space, it is possible for a distributed sensor to measure the overall structural vibration information of an examined target structure. Measurement of force distribution in the structure in the sensed extent is also possible. However, since different distributed sensor configurations have to be implemented costly for the measurement of different target structures, the design and construction efforts in these distributed sensors therefore limit their application.
Based on traditional piezoelectricity theories, gain and phase characteristics for electrical signals detected in piezoelectric devices, either those for mechanical vibration sensing or those for electrical signal filtering, are inter-dependent. The inter-relationship between the gain and phase characteristics for piezoelectric devices that has been difficult to control have placed limitations on their design.
It is therefore an object of the present invention to provide a piezoelectric transducer apparatus having independent gain and phase characteristic functions.
The present invention achieves the above and other objects by providing a piezoelectric transducer apparatus that comprises at least one piezoelectric unit and a body structure. Each of the at least one piezoelectric unit has a piezoelectric block and at least one pair of electrodes. Each electrode is adhered to one surface of the piezoelectric block. Each of the at least one piezoelectric unit is adhered to the surface of the body structure with the electrode exposed externally. The transducer apparatus has a generalized sensor equation which can be modeled in a fourth-order partial differential equation mathematical system. At least one of the electrodes or the piezoelectric block of each of the at least one piezoelectric unit has a shape matched to a desired body strain pattern existing in the body structure wherein the electrode of each of the at least one piezoelectric unit may excite a strain pattern in the body structure that is the same as the desired body strain pattern. The body structure of any structural configuration may have a resolved electrode shape that results in the disengagement of the phase and gain characteristics of the piezoelectric construction based on that particular body structure.